Back to EveryPatent.com
United States Patent |
6,183,893
|
Futamoto
,   et al.
|
February 6, 2001
|
Perpendicular magnetic recording medium and magnetic storage apparatus
using the same
Abstract
The present invention relates to a perpendicular magnetic recording medium
and a magnetic storage apparatus which are improved to be suitable for
high-density magnetic recording. An object thereof is to provide the
perpendicular magnetic recording medium and the magnetic storage apparatus
which have a low noise property for realizing a recording density of 10
Gb/in..sup.2 or more and a high stability against thermal fluctuation.
The perpendicular magnetic recording medium comprising a perpendicular
magnetic film formed through an underlayer on a nonmagnetic substrate,
wherein the underlayer comprises a material having a hexagonal close
packed structure or an amorphous structure, and has a first underlayer
nearer to the substrate, and a second underlayer having a hexagonal close
packed structure formed on the first underlayer and a preferred growth
orientation of [0001] and comprising a material capable of hetero-epitaxy
growth onto the perpendicular magnetic film.
Inventors:
|
Futamoto; Masaaki (Tsukui-gun, JP);
Hirayama; Yoshiyuki (Kodaira, JP);
Ito; Kenya (Hachioji, JP);
Yoshida; Kazuetsu (Hidaka, JP);
Honda; Yukio (Fuchu, JP);
Inaba; Nobuyuki (Hasuda, JP)
|
Assignee:
|
Hitachi, Ltd. (Tokyo, JP)
|
Appl. No.:
|
285751 |
Filed:
|
April 5, 1999 |
Foreign Application Priority Data
| Apr 19, 1998[JP] | 10-093334 |
| Jun 15, 1998[JP] | 10-167089 |
Current U.S. Class: |
428/831.2; 360/81; 427/131; 427/132; 428/336; 428/668; 428/670; 428/900; 428/928 |
Intern'l Class: |
B32B 015/00 |
Field of Search: |
428/694 TS,694 TM,900,928,336,670,668
360/81
427/131,132
|
References Cited
Foreign Patent Documents |
57-109127 | Jul., 1982 | JP.
| |
58-77025 | May., 1983 | JP.
| |
58-14135 | Aug., 1983 | JP.
| |
60-64413 | Apr., 1985 | JP.
| |
60-214417 | Oct., 1985 | JP.
| |
Other References
41st Annual Conference on Magnetism and Magnetic Materials, Nov. 1996,
Abstracts, DQ-13, p. 116.
41st Annual Conference on Magnetism and Magnetic Materials, Nov. 1996,
Abstracts EB-12, pp. 133-134.
The 5th Perpendicular Magnetic Recording Symposium PMRS '96, Oct. 1996, pp.
95-100.
IEEE Transactions, MAG-24, No. 6, 1988, pp. 2706-2708. (no month avail.).
|
Primary Examiner: Pianalto; Bernard
Attorney, Agent or Firm: Mattingly, Stanger & Malur, P.C.
Claims
What is claimed is:
1. A perpendicular magnetic recording medium having a perpendicular
magnetic film formed through an underlayer on a nonmagnetic substrate,
the underlayer which includes a material having a hexagonal close packed
structure or an amorphous structure, comprising:
a first underlayer nearer to the substrate; and
a second underlayer having a hexagonal (close packed structure formed on
the first underlayer, a preferred growth of [0001] and a material capable
of hetero-epitaxy growth onto the perpendicular magnetic film,
wherein the perpendicular magnetic film formed on the second underlayer
includes a lower perpendicular magnetic layer contacting the second
underlayer and an upper perpendicular magnetic layer formed thereon, the
perpendicular magnetic film including the lower and upper layers is a
Co-alloy polycrystal film, the total concentration of added nonmagnetic
elements in the upper perpendicular magnetic layer is lower than that in
the lower perpendicular magnetic layer, the saturation magnetization Ms
and the magnetic anisotropic energy Ku of the upper perpendicular magnetic
layer are larger that those of the lower perpendicular magnetic layer,
continues hetero-epitaxy growth from the second underlayer to the upper
perpendicular magnetic layer is realized, the total thickness of the
perpendicular magnetic film is from 5 to 70 nm, and the average grain size
of crystal grains in the upper perpendicular magnetic layer is from 5 to
15 nm on the basis of measurement at the surface side of the upper
perpendicular magnetic layer.
2. A perpendicular magnetic recording medium according to claim 1, wherein
a nonmagnetic layer or a magnetic layer having a saturation magnetization
Ms of 50 emu/cc or less is formed as an interlayer between the lower
perpendicular magnetic layer and the upper perpendicular magnetic layer,
and continuous hetero-epitaxy growth from the second underlayer to the
upper perpendicular magnetic layer is made.
3. A perpendicular magnetic recording medium according to claim 1, wherein
a metal film of 0.1-5 nm thickness is formed on the upper perpendicular
magnetic layer and the metal film is any one metal film among a film of a
simple metal selected from the element group comprising Pt, Pd, Ir, Re, Ru
and Hf; an alloy film made mainly of any one of these metal elements;
stack films of a Co film or a Co-alloy film, and a film of a simple metal
selected from the element of these metal elements or an alloy film made
mainly of any one of these metal elements; and an amorphous magnetic
material film containing a rare-earth element.
4. A perpendicular magnetic recording medium according to claim 1, wherein
the lower perpendicular magnetic layer is a polycrystal layer having a
segregation phase containing a nonmagnetic element in an amount of 25
atomic % or more inside its crystal grain boundary.
5. A perpendicular magnetic recording medium according to claim 1, wherein
the magnetic anisotropic energy of the lower perpendicular magnetic layer
is from 1.times.10.sup.6 to 2.5.times.10.sup.6 erg/cc and the magnetic
anisotropic energy of the upper perpendicular magnetic layer is from
2.5.times.10.sup.6 to 5.times.10.sup.6 erg/cc.
6. A perpendicular magnetic recording medium according to claim 1, wherein
the difference between the lattice constant of the second underlayer and
that of the lower perpendicular magnetic layer is 5% or less.
7. A perpendicular magnetic recording medium according to claim 1, wherein
the thickness of the lower perpendicular magnetic layer is 2 or more times
as large as that of the upper perpendicular magnetic layer.
8. A perpendicular magnetic recording medium having a perpendicular
magnetic film formed through an underlayer on a nonmagnetic substrate,
the underlayer which includes a material having a hexagonal close packed
structure or an amorphous structure, comprising:
a first underlayer nearer to the substrate; and
a second underlayer having a hexagonal close packed structure formed on the
first underlayer, a preferred growth orientation of [0001] and a material
capable of hetero-epitaxy growth onto the perpendicular magnetic film,
wherein the perpendicular magnetic film formed on the second underlayer
includes a lower perpendicular magnetic layer contacting the second
underlayer and an upper perpendicular magnetic layer formed thereon, the
perpendicular magnetic film including the lower and upper layers is a
Co-alloy polycrystal film, the total concentration of added nonmagnetic
elements in the upper perpendicular magnetic layer is lower than that in
the lower perpendicular magnetic layer, the saturation magnetization Ms
and the magnetic anisotropic energy Ku of the upper perpendicular magnetic
layer are larger that those of the lower perpendicular magnetic layer,
continuos hetero-epitaxy growth from the second underlayer to the upper
perpendicular magnetic layer is made, the total thickness of the
perpendicular magnetic film is from 5 to 70 nm, and the average grain size
of crystal grains in the upper perpendicular magnetic layer is from 5 to
15 nm on the basis of measurement at the surface side of the upper
perpendicular magnetic layer; and
a nonmagnetic layer or a magnetic layer having a saturation magnetization
Ms of 50 emu/cc or less is formed as an interlayer between the lower
perpendicular magnetic layer and the upper perpendicular magnetic layer,
and continuous hetero-epitaxy growth from the second underlayer to the
upper perpendicular magnetic layer is made.
9. A perpendicular magnetic recording medium according to claim 8, wherein
a metal film of 0.1-5 nm thickness is formed on the upper perpendicular
magnetic layer and the metal film is any one metal film among a film of a
simple metal selected from the element group comprising Pt, Pd, Ir, Re, Ru
and Hf; an alloy film made mainly of any one of these metal elements;
stack films of a Co film or a Co-alloy film, and a film of a simple metal
selected from the element of these metal elements or an alloy film made
mainly of any one of these metal elements; and an amorphous magnetic
material film containing a rare-earth element.
10. A perpendicular magnetic recording medium according to claim 8, wherein
the lower perpendicular magnetic layer is a polycrystal layer having a
segregation phase containing a nonmagnetic element in an amount of 25
atomic % or more inside its crystal grain boundary.
11. A perpendicular magnetic recording medium according to claim 8, wherein
the magnetic anisotropic energy of the lower perpendicular magnetic layer
is from 1.times.10.sup.6 to 2.5.times.10.sup.6 erg/cc and the magnetic
anisotropic energy of the upper perpendicular magnetic layer is from
2.5.times.10.sup.6 to 5.times.10.sup.6 erg/cc.
12. A perpendicular magnetic recording medium according to claim 8, wherein
the difference between the lattice constant of the second underlayer and
that of the lower perpendicular magnetic layer is 5% or less.
13. A perpendicular magnetic recording medium according to claim 8, wherein
the thickness of the lower perpendicular magnetic layer is 2 or more times
as large as that of the upper perpendicular magnetic layer.
14. A perpendicular magnetic recording medium according to claim 8, wherein
the thickness of the magnetic layer as the interlayer is from 0.1 to 5 nm.
15. A magnetic storage apparatus comprising:
a magnetic recording medium;
a spindle motor for rotating the magnetic recording medium;
a magnetic head having a recording element; and
a reading element, an actuator for positioning the magnetic head, and a
means for processing reading/recording signals of the magnetic head,
wherein the perpendicular magnetic recording medium comprises a
perpendicular magnetic film formed through an underlayer on a nonmagnetic
substrate,
the underlayer which includes a material having a hexagonal close packed
structure or an amorphous structure, comprises: a first underlayer nearer
to the substrate; and a second underlayer having a hexagonal close packed
structure formed on the first underlayer, a preferred growth orientation
of [0001] and a material capable of hetero-epitaxy growth onto the
perpendicular magnetic film,
the perpendicular magnetic film formed on the second underlayer includes a
lower perpendicular magnetic layer contacting the second underlayer and an
upper perpendicular magnetic layer formed thereon, the perpendicular
magnetic film including the lower and upper layers is a Co-alloy
polycrystal film, the total concentration of added nonmagnetic elements in
the upper perpendicular magnetic layer is lower than that in the lower
perpendicular magnetic layer, the saturation magnetization Ms and the
magnetic anisotropic energy Ku of the upper perpendicular magnetic layer
are larger that those of the lower perpendicular magnetic layer, continuos
hetero-epitaxy growth from the second underlayer to the upper
perpendicular magnetic layer is made, the total thickness of the
perpendicular magnetic film is from 5 to 70 nm, and the average grain size
of crystal grains in the upper perpendicular magnetic layer is from 5 to
15 nm on the basis of measurement at the surface side of the upper
perpendicular magnetic layer.
16. A magnetic storage apparatus according to claim 15, wherein the reading
element of the magnetic head comprises a megnetoresistive transducer or a
giant magnetoresistive transducer, and has a function of performing
magnetic recording/reading at an areal recording density of 10
Gb/in..sup.2 or more.
17. A magnetic storage apparatus according to claim 15, wherein the reading
element of the magnetic head comprises a magneto-resistance detection type
head using magnetic tunneling effect, and has a function of performing
magnetic recording/reading at an areal recording density of 30
Gb/in..sup.2 or more.
18. A perpendicular magnetic recording medium comprising a magnetic
recording film having the property of perpendicular easy magnetization and
being formed through an underlayer on a nonmagnetic substrate,
wherein a magnetic film or magnetic films having the property of in-plane
easy magnetization is/are formed on both surfaces or a single surface of
the magnetic recording film.
19. A perpendicular magnetic recording medium according to claim 18,
wherein the thickness of the magnetic film having the property of in-plane
easy magnetization is 10 nm or less.
20. A perpendicular magnetic recording medium according to claim 18,
wherein the magnetic film having the property of in-plane easy
magnetization has a coercive force, measured along its longitudinal
direction, of 100 Oe or more.
21. A perpendicular magnetic recording medium according to claim 18,
wherein the magnetic film having the property of in-plane easy
magnetization is a Sm--Co magnetic film, or an Fe--Nd--B magnetic film.
22. A magnetic storage apparatus comprising:
a magnetic recording medium;
an actuator for rotating and driving the magnetic recording medium;
a magnetic head for recording and reaching;
a means for moving the magnetic head relatively to the magnetic recording
medium; and
a means for reading output signals from the magnetic head,
wherein the perpendicular magnetic recording medium has a magnetic
recording film having the property of perpendicular easy magnetization and
being formed through an underlayer on a nonmagnetic substrate, and a
magnetic film or magnetic films having the property of in-plane easy
magnetization is/are formed on both surfaces or a single surface of the
magnetic recording film.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium
having a perpendicular magnetic film suitable for high-density magnetic
recording, and a magnetic storage apparatus using the same.
2. Description of the Prior Art
In magnetic disk apparatuses that have been made practicable at present,
longitudinal magnetic recording is commercialized. In the longitudinal
magnetic recording, a technical objective is to form, in a longitudinal
magnetic recording medium which is liable to be magnetized in the
direction parallel to its disk substrate surface, longitudinal magnetic
domains that are parallel to the substrate at high densities. As a method
to increase the recording density of this longitudinal magnetic recording
medium, there is proposed a method of using keepered media in which a very
thin, soot magnetic film is formed on the surface of a recording medium
having an axis of easy magnetization in the longitudinal direction.
This technique is described on page 116 (Article No. DQ-13) and page 133
(Article No. EB-12) of collected abstracts published in 41st Annual
Conference of Magnetism &Magnetic Materials (Nov. 12-15, 1996), and the
like.
It is stated that according to adoption of such a medium structure it is
possible to use an inductive type of thin film head for recording and
reading so as to improve the areal recording density of magnetic recording
greater than 1 Gb/in..sup.2 In the case of the longitudinal recording
system, however, the magnetization directions of adjacent recorded bits
are essentially opposite to each other. Thus, even if such a technique is
used, magnetization transition areas whose boundary has a certain width
are formed, so that it is technically not easy to realize an areal
recording density of 10 Gb/in..sup.2 or more.
On the other hand, the perpendicular magnetic recording is a method to form
magnetization perpendicular to the thin film media surface, and is
different from conventional longitudinal recording media in recording
principles and the mechanisms of medium noises. Since adjacent
magnetization directions are not opposite to each other, the perpendicular
magnetic recording has attracted attention as a method suitable for
high-density magnetic recording. Various structures of perpendicular media
are proposed to improve the performance of magnetic recording.
In order to improve perpendicular orientation of a perpendicular magnetic
film composed of, for example, Co alloy materials, investigations have
been made on methods of forming an underlayer between the perpendicular
magnetic film and a substrate. For example, Japanese Unexamined Patent
Publication Nos. 58-77025 and 58-141435 disclose methods of forming a Ti
film as an underlayer of a Co--Cr magnetic film. Japanese Unexamined
Patent Publication No. 60-214417 discloses a method of using a Ge or Si
material as an underlayer, and Japanese Unexamined Patent Publication No.
60-064413 discloses underlayer materials of oxides such as CoO and NiO.
Moreover, as a perpendicular magnetic recording medium which is combined
with a single pole type recording head for use, investigations have been
made on a medium having a soft magnetic thin film such as permalloy
between its substrate and its perpendicular magnetic film.
SUMMARY OF THE INVENTION
For a perpendicular magnetic recording medium capable of high-density
recording at a level of 10 Gb/in..sup.2 or more, it is necessary that its
linear recording density resolution is large and further medium noises are
small.
Reports up to the present state that it is effective to make the thickness
of a perpendicular magnetic film small, to introduce a nonmagnetic CoCr
underlayer between a perpendicular magnetic film and a substrate, to add a
nonmagnetic element such as Ta as an additive element to a Co alloy
magnetic film, or to make the grain size of magnetic crystals smaller, as
described in the article titled "High S/N single-layered perpendicular
magnetic recording disks" on pp. 95-100 of collected conference materials
of 5th Perpendicular Magnetic Recording Symposium (Oct. 23-25, 1996).
Such countermeasures make it possible to reduce medium noises considerably.
If the noises cain be further reduced, it is possible to increase the
recording density of magnetic recording apparatuses with ease.
In consideration of such situations of perpendicular magnetic recording, a
first object of the present invention is to provide a perpendicular
magnetic recording medium having a low noise property for implementing a
high recording density of 10 Gb/in..sup.2 or more, and a high-density
magnetic storage apparatus using the medium.
As described in Japanese Unexamined Patent Publication No. 57-109127, the
Journal of the Japan Applied Magnetism Society Vol. 8, No. 2, pp. 57-60
(1984), or IEEE Trans., MAG-24, No. 6, pp. 2706-2708 (1988), a Co--Cr
based alloy films are used as a perpendicular magnetic recording medium,
and it appears preferable to segregate nonmagnetic Cr atoms in the grain
boundary of fine grains constituting the medium. This is because areas
having a high Cr concentration are formed in the surface of the grains to
improve corrosion resistance, and further nonmagnetic Cr atoms are
segregated in the grain boundary in the same manner as in the longitudinal
recording media so that magnetic exchange interaction between the grains
is broken off, whereby magnetic domains are made finer to reduce medium
noises.
In the combination of a ring type head and a single layer perpendicular
magnetic medium, however, even if the medium is manufactured under
conditions for promoting segregation of Cr atoms, the resultant medium is
not necessarily strong against thermal fluctuation. This does not bring
out advantages of perpendicular magnetic recording.
Therefore, a second object of the present invention is to provide a
magnetic recording medium having stability against thermal fluctuation,
and a high-density magnetic recording apparatus using the same. (1) First,
the following inventions will be described: a perpendicular magnetic
recording medium having a low noise property for realizing a high
recording density, which can attain the first object of the present
invention, and a high-density magnetic recording apparatus using the same.
Examination of recorded magnetization of perpendicular magnetic recording
media with a magnetic force microscope and a spin polarized scanning
electron microscope has proved that most of noises are caused by reversed
domains, which are present in the surface of the media and will be
described in detail later, and microscopic fluctuation of magnetization.
The microscopic fluctuation of magnetization means that the intensity of
the local magnetization fluctuates at intervals of about 0.2-10 .mu.m from
area to area on the medium surface. In order to reduce medium noises, it
is essential not only to reduce the reversed domains but also to reduce
the microscopic fluctuation of magnetization present in the surface of the
media.
From the results of experiments by the inventors et al., it has been made
clear that the object can be attained by the following method.
That is, when a perpendicular magnetic film is magnetized perpendicularly
to the film plane and in a single direction, an intense demagnetizing
field acts on the medium surface. Under the influence of this
demagnetizing field, there are formed so-called reversed domains, which
are along the direction reverse to the perpendicular magnetization
direction. In order to prohibit the forming of these reversed domains, it
is necessary to adopt a perpendicular magnetic film having a large
magnetic anisotropic energy.
It is desired that the magnetic anisotropic energy is 2.5.times.10.sup.6
erg/cc or more. The maximum value of the magnetic anisotropic energy of a
perpendicular magnetic film using a Co-alloy material, which can easily be
handled as a practical medium, is 5.times.10.sup.6 erg/cc. There exist
Co-alloy materials with ordered lattice structure which have a larger
magnetic anisotropic energy than the value. However, a process temperature
of 500.degree. C. or higher becomes necessary for obtaining an ordered
phase, so that the following problems arise: the scope from which a
substrate material is selected gets narrow, or crystal grains constituting
the magnetic film grow coarse so that it becomes difficult to reduce
noises.
In perpendicular magnetic films made of a multilayer film of materials
other than Co-alloys, such as Pt/Co or Pd/Co, or perpendicular magnetic
films having an amorphous structure containing rare-earth elements such as
TbFeCo, all of their magnetic anisotropic energies are 2.5.times.10.sup.6
erg/cc or more. Thus, they can be used as materials for attaining the
object of the present invention. However, since they themselves have an
intense in-plane magnetic interaction so that medium noises become large,
any solutions are required for them to reduce the medium noises.
In order to make the areal density of magnetic recording to a value of 10
Gb/in..sup.2 or more, it is necessary that its liner recording density is
300 kFCI (Flux Change per Inch) or more. The bit length corresponding to
this linear recording density is 83 nm. Considering the recording
capability of a ring type head, it is desired a that the thickness of the
magnetic recording medium taking charge in recording is smaller than the
shortest bit length. It is necessary to set the thickness of the
perpendicular magnetic film to 70 nm or less. If the thickness is 5 nm or
less, recording magnetization is made unstable because of thermal
fluctuation. As a result, the thickness of the perpendicular magnetic film
suitably ranges from 5 to 70 nm.
The intensity of the reversed domains, which cause noises, depends on the
grain size of the polycrystal film constituting a perpendicular magnetic
recording medium and the strength of magnetic interaction between the
crystal grains. To make the size of the reversed domains to not more than
a bit length of300 kFCI, it has been proved that the average of the
crystal grain size needs to be 15 nm or less. However, if the crystal
grain size becomes too small, the coercive force of the medium decreases
so that the medium becomes unsuitable for a recording medium. It is
therefore desired that the grain size is 5 nm or more. The average of the
crystal grain size, referred to in the present invention, means the
average of circles having an area equivalent to the area of crystal grains
observed on the surface of a magnetic recording medium.
By using a perpendicular magnetic film having a high magnetic anisotropic
energy, since the generation of reversed domains can be prohibited, it is
possible to reduce the medium noises resulting from the formation of
reversed domains. As other cause of the medium noises, however, there is
known microscopic fluctuation of the magnetization present in the surface
of the medium. In a case there exists a considerable in-plane magnetic
interaction across the magnetic film, a long range magnetization
fluctuation arises. In a case where the surface of the perpendicular
magnetic film has magnetic inhomogenity, a short range magnetization
fluctuation arises. It has been proved that both the fluctuations cause
medium noises and that, in order to suppress such long and short range
fluctuations of the magnetization, it is necessary to make the
perpendicular magnetic film to be consisting of a bilayer structure, and
adopt as the upper layer a perpendicular magnetic layer having a large
magnetic anisotropic energy (Ku) and as the lower layer a perpendicular
magnetic layer having both of a small magnetic anisotropic energy and
promoted magnetic isolation between crystal grains.
It is effective that the upper perpendicular magnetic layer satisfies:
2.5.times.10.sup.6 erg/cc.ltoreq.Ku.ltoreq.5.times.10.sup.6 erg, and the
lower perpendicular magnetic layer satisfies: 1.times.10.sup.6
erg/cc.ltoreq.Ku.ltoreq.2.5.times.10.sup.6 erg.
The lower perpendicular magnetic layer functions to make the pitch of the
microscopic fluctuation of the magnetization finer than the bit length
that is used for recording, and the upper perpendicular magnetic layer
functions to suppress the forming of reversed domains. Concerning the
ratio of the thickness of both the films, the thickness of the lower layer
is desirably larger than that of the upper layer to suppress noises
produced from the whole of the layers, and the former is preferably two or
more times as large as the latter. It is not desirable that the former is
less than two times as large as the latter, because the lower layer does
not sufficiently attain the function for making the pitch of the
microscopic fluctuation of the magnetization finer than the bit length
that is used for recording.
Concerning the lower perpendicular magnetic layer, it is desired that the
average of its crystal grain sizes is from 5 to 15 nm and that, for
reducing the magnetic interaction between its crystal grains nonmagnetic
elements are precipitated in an amount of 25 atomic % or more, or voids
are formed, in the crystal grain boundary. When the total amount of the
nonmagnetic additive elements contained in the Co-alloy constituting the
perpendicular magnetic film is not less than 25 atomic % and practically
not more than 50%, the saturation magnetization Ms of the material
decreases extremely. In case of some additive elements, the film changes
to non-magnetic. It is undesireble that the total amount of the
nonmagnetic additive element is over 50%, because it becomes difficult to
keep the hexagonal close packed structure of Co. If such a low saturation
magnetization layer or a nonmagnetic layer is present, the magnetic
exchange interaction between the magnetic crystal grains is lowered to
produce a desirable effect of the reduction in medium noises.
In order that the magnetic recording film has an intense perpendicular
magnetic anisotropy, it is necessary that crystal lattices of the upper
and lower perpendicular magnetic layers are continuous, that is, it is
necessary to maintain hetero-epitaxy relationship.
In order to reduce medium noises, it is also effective, adding to the
reduction of magnetic interact-on between the magnetic crystal grains, to
magnetically isolate and/or to reduce the magnetic interaction of the
crystal grains in the thickness direction of the perpendicular magnetic
film. For this purpose, it is effective to introduce, between the two
upper and lower perpendicular magnetic layers, an interlayer with
non-magnetic property, or with weak magnetization of which saturation
magnetization Ms is 50 emu/cc or less.
The thickness of the interlayer suitably ranges from 0.1 to 5 nm. If the
thickness of the interlayer is less than 0.1 nm, an effect based on the
introduction of the interlayer cannot be sufficiently obtained. If it is
over 5 nm, the coercive force of the whole of the medium is unfavorably
lowered. Suitable materials of the interlayer are a simple metal such as
Pt, Pd, Ir, Re, Ru or Hf; alloys made mainly of such a metal element; and
materials wherein the metal or other nonmagnetic element is added in an
amount of 25 atomic % or mores to Co.
Through thermal activation, the reversed domains formed in the surface of
the perpendicular magnetic film increase caused by demagnetization field
as time passes. Results of the inventors' experiments have made it evident
that in order to suppress the forming of the reversed domains following
the passage of time it is effective to form a thin metal film of which
thickness ranging between 0.1 and 5 nm on the surface of the upper
magnetic layer, or at the substrate side of the lower perpendicular
magnetic layer, as well as on the upper film.
As this metal film, the following can be used: a simple metal selected from
the element group consisting of Pt, Pd; Ir, Re, Ru and Hf; alloy films
made mainly of any one(s) of these metal elements; laminated films of a Co
film or a Co-alloy film, and a film of the metal or an alloy film made
mainly of the metal element described above; an amorphous magnetic
material film containing a rare-earth element; soft magnetic films such as
permalloy, Fe--Si, Fe--Si--Al, and Co--Nb--Zr; or magnetic films which can
easily be magnetized longitudinally, such as Co, Ni, Fe, Co--Ni,
Co--Ni--Cr. Instead of forming the metal film, a light element such as C,
B, N or P may be diffused or ion-implanted onto the surface of the
perpendicular magnetic film, so that apart of the perpendicular magnetic
film, which is at its surface side viewed in the thickness direction, may
be changed into a soft magnetization film or an longitudinal magnetic
film.
Summarizing the above, the present invention is as follows.
The perpendicular magnetic recording medium of the present invention
comprises a perpendicular magnetic film formed through an underlayer on a
nonmagnetic substrate, wherein the underlayer comprises a material having
a hexagonal close packed structure or an amorphous structure. The
underlayer has a first underlayer nearer to the substrate, and a second
underlayer having a hexagonal close packed structure formed on the first
underlayer and a preferred growth of [0001] and comprising a material
capable of hetero-epitaxy growth to the perpendicular magnetic film which
is subsequently formed on the second underlayer. The perpendicular
magnetic film formed on the second underlayer includes a lower
perpendicular magnetic layer contacting the second underlayer and an upper
perpendicular magnetic layer formed thereon, the perpendicular magnetic
film including the lower and upper layers is a Co-alloy polycrystal film,
and the total concentration of added nonmagnetic elements in the upper
perpendicular magnetic layer is lower than that in the lower perpendicular
magnetic layer. The saturation magnetization Ms and the magnetic
anisotropic energy Ku of the upper perpendicular magnetic layer are larger
that those of the lower perpendicular magnetic layer, and continues
hetero-epitaxy growth from the second underlayer to the upper
perpendicular magnetic layer is realized. The total thickness of the
perpendicular magnetic film is from 5 to 70 nm, and the average grain size
of crystal grains in the upper perpendicular magnetic layer is from 5 to
15 nm on the basis of measurement at the surface side of the upper
perpendicular magnetic layer.
Continuous hetero-epitaxy growth (growth of films with continuity of the
crystal lattices) from the second underlayer to the upper perpendicular
magnetic layer may be realized by disposing a nonmagnetic interlayer or an
interlayer having a saturation magnetization Ms of 50 emu/cc or less
between the lower perpendicular magnetic layer and the upper perpendicular
magnetic layer. The interlayer has a thickness of 0.1-5 nm.
A metal film having a thickness of 0.1-5 nm may be deposited on the upper
perpendicular magnetic layer. This metal film may be made of a film of a
simple metal selected from the element group consisting of Pt, Pd, Ir, Re,
Ru and Hf; an alloy film made mainly of any one(s) of these metal
elements; laminated films of a Co film or a Co-alloy film, and a film of a
simple metal selected from the element group consisting of Pt, Pd, Ir, Rg,
Ru and Hf or an alloy film made mainly of any one(s) of these metal
elements; or an amorphous magnetic material film containing a rare-earth
element.
It is preferred that the lower perpendicular magnetic layer is a
polycrystal layer containing, in its crystal grain boundary, a segregation
phase of a nonmagnetic element in an amount of 25 atomic % or more and
practically 50 atomic % or less. It is preferred that the magnetic
anisotropic energy Ku of the lower perpendicular magnetic layer is not
less than 1.times.10.sup.6 erg/cc a and not more than 2.5.times.10.sup.6
erg/cc, and the magnetic anisotropic energy Ku of the upper perpendicular
magnetic layer is not less than 2.5.times.10.sup.6 erg/cc and not more
than 5.times.10.sup.6 erg/cc.
It is preferred that the difference between the lattice constants of the
second underlayer and the lower perpendicular magnetic layer is 5% or
less, and the thickness of the lower perpendicular magnetic layer is 2 or
more times as large as that of the upper perpendicular magnetic layer. In
a case where the structure is used and additionally a magnetic film such
as a soft magnetic layer or an in-plane magnetic film is inserted between
the underlayer and the substrate, likewise the advantages of the present
invention can be obtained.
The perpendicular magnetic recording medium of the present invention is
applied to magnetic recording apparatuses so as to exhibit a high
performance.
Namely, a magnetic storage apparatus of the present invention comprises a
magnetic recording medium, a spindle motor for rotating the magnetic
recording medium, a magnetic head having a recording element and a reading
element, an actuator for positioning the magnetic head, and a means for
signal processing or reading signals of the magnetic head. The
perpendicular magnetic recording medium is used as the magnetic recording
medium, and a magnetoresistive transducer or a giant megnetoresistive
transducer is used as the reading element of the magnetic head, thereby
performing magnetic recording or reading at an areal recording density of
10 Gb/in..sup.2 or more.
Furthermore, another magnetic storage apparatus of the present invention
comprises a magnetic recording medium, a spindle motor for rotating the
magnetic recording medium, a magnetic head having a recording element and
a reading element, an actuator for driving the magnetic head, and a means
for signal processing or reading signals of the magnetic head. The
perpendicular magnetic recording medium of the present invention is used
as the magnetic recording medium, and a magneto-resistance detection type
head using magnetic tunneling effect is used as the reading element of the
magnetic head, thereby performing magnetic recording or reading at an
areal recording density of 30 Gb/in..sup.2 or more.
According to the present invention, noises of the perpendicular magnetic
recording medium can be reduced, so that a high S/N ratio can be obtained,
resulting in implementing high-density magnetic disk devices. In
particular, magnetic recording which can exhibit a high density of 10
Gb/in..sup.2 or more can be realized to easily make the devices compact
and make their capacity larger. (2) The following will describe a magnetic
recording medium having stability against thermal fluctuation, which can
attain the second object of the present invention, and a high-density
magnetic recording apparatus using the same.
From eager investigations on the relationship between magnetic read/write
characteristics and the properties of a medium, the inventors have found
that the stability against thermal fluctuation is closely related to the
magnetic property of the topmost surface area of the recording layer, and
then arrived the present invention.
In other words, in a magnetic film that is widely used in perpendicular
magnetic recording, for example, a Co--Cr based alloy perpendicular
magnetic film, the magnetic anisotropy of its topmost surface layer is
smaller than that of the interior of the film. Consequently, seeds of
reversed domains are first produced in the topmost surface and become
nuclei, so that the reversed domains are conducted to the interior of the
film. For this reason, the intensity of the magnetic field generated by
the reversed domains decreases so that a thermally unstable structure is
produced. In order to prevent this, it is effective to deposit a film
having an large perpendicular magnetic anisotropy on the surface of the
recording film. However, it is necessary to use a material having a far
larger magnetic anisotropy constant than that of Co--Cr based alloys. Such
a material is very restrictive among all materials and is, for example,
Co--Pt based materials.
In the present invention, the object can be attained by forming, on both
surfaces or one side surface of a perpendicular magnetic recording film, a
magnetic film having such the property with longitudinal easy
magnetization that the coercive force of the magnetization curve measured
along the longitudinal direction is 100 Oe or more, and more preferably
500 Oe or more. Sm--Co based magnetic films or Fe--Nd--B based magnetic
films, which have a large anisotropy constant and are not liable to be
affected thermal fluctuation, are especially suitable for the magnetic
films having such the property of longitudinal easy magnetization.
That is, in a recording medium used in perpendicular magnetic recording, a
magnetic film having the property of longitudinal easy magnetization is
formed on both surface or a single surface of a magnetic recording film
having the property of easy perpendicular magnetization. This magnetic
film having the property of longitudinal easy magnetization is a film for
prohibiting the formation of reversed domains in the surface layer portion
of the perpendicular magnetic recording film, and can be called a
prohibitive layer to nucleate reverse domains.
The thickness of the magnetic film having the property of longitudinal easy
magnetization is preferably 10 nm or less and more preferably about 1 nm.
If the thickness is too large, components which are longitudinally
recorded become large to damage the advantages of perpendicular magnetic
recording.
Concerning the magnetic film having the property of longitudinal easy
magnetization, the coercive force measured along the longitudinal
direction is preferably 100 Oe or more and more preferably 500 Oe or more.
Furthermore, it is desired that the upper limit thereof is 4,000 Oe or
less in the light of recording capability of a recording head. If the
coercive force is less than 100 Oe, magnetic walls are liable to be
produced in the longitudinal magnetization film to cause noises.
Sm--Co based magnetic films or Fe--Nd--B based magnetic films are suitable
for the magnetic film having the property of longitudinal easy
magnetization. In the Sm--Co based magnetic films, a high coercive force
can be obtained by setting its composition in such a manner that the Sm
content is from 15 to 22 atomic %, and more preferably from 18 to 20
atomic %. Concerning the Fe--Nd--B based magnetic films, its composition
is preferably a composition that Nd is from 10 to 35 atomic % and B is
from 5 to 20 atomic %, and more preferably a composition that Nd is from
10 to 15 atomic 5 and B is from 5 to 10 atomic %.
According to the present invention, in a Co--Cr based film medium for
perpendicular magnetic recording, stability against thermal fluctuation is
improved by disposing a very thin film with longitudinal easy
magnetization on the surface of the perpendicular magnetic recording film.
Furthermore, a high reproduced output and a low medium noise property can
be obtained as a secondary effect to improve an S/N ratio. Moreover, the
magnetic recording/reading apparatus using the perpendicular magnetic
recording medium of the present invention has a high reproduced output and
S/N ratio, and an excellent capability of storing recorded data for a
longer time.
The following preferred examples and drawings for reference will make clear
structural characteristics of the present invention and industrially
availability.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view of main elements of a recording medium
of an example according to the present invention.
FIG. 2 is a view illustrating another example according to the present
invention, and is a schematic sectional view of main elements of a
recording medium wherein an interlayer is formed between an upper
perpendicular magnetic layer and a lower perpendicular magnetic layer.
FIG. 3 is a view illustrating still another example according to the
present invention, and is a schematic sectional view of main elements of a
recording medium wherein a metal layer is formed on the upper
perpendicular magnetic layer shown in FIG. 1.
FIG. 4 is a view illustrating other example according to the present
invention, and is a schematic sectional view of main elements of a
recording medium wherein a metal layer is formed on the upper
perpendicular magnetic layer shown in FIG. 2.
FIG. 5A is a plane view of a structure of a magnetic storage apparatus, and
FIG. 5B is a sectional view thereof.
FIG. 6 shows magnetization curves of a sample of the present invention
wherein a longitudinal easy magnetization film is deposited on the surface
of a perpendicular magnetic recording medium and a comparative sample.
FIG. 7 is a block view which schematically illustrates an example of the
magnetic recording/reading apparatus of the present invention, and which
includes a partial cross section.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, examples of the present invention will be
specifically described hereinafter.
FIG. 1 is a schematic sectional view of a first example of the
perpendicular magnetic recording medium according to the present
invention. In this perpendicular magnetic recording medium, a
perpendicular magnetic film is formed on a nonmagnetic substrate 11
through underlayers 12 and 13 for improving perpendicular orientation of
the magnetic film and controlling its crystal grain sizes.
The first underlayer 12 formed at the side of substrate functions so as to
control nucleation process of the film during thin film growth in a manner
that the growth orientation of the second underlayer 13 having a hexagonal
close packed structure becomes [0001] orientation. The following are
suitable for the material of the first underlayer 12 fitting to this
function: Ti or Ru; materials containing this element as a main element
and Cr, V, Mo or W as an additive element and having a hexagonal close
packed structure; amorous materials consisting of Si or Ge, or made mainly
of this element.
The second underlayer 13 is made of a nonmagnetic material having a
hexagonal close packed structure or a weak magnetic material having a
hexagonal close packed structure and having a saturation magnetization Ms
of 50 emu/cc or less. As this material, there is used a material wherein a
nonmagnetic element such as Cr, V-Mo, W, Nb, Re, Ti or Y is added in an
amount of 25 atomic % or more and practically 50 atomic % or less to Co.
It is unfovarable that the intensity of the magnetization of this material
is 50 emu/cc or more, because resolution at the time of recording or
reading is lowered or noises are increased. This second underlayer and the
perpendicular magnetic film 14 formed thereon keeps hetero-epitaxy
relationship. In order to realize good hetero-epitaxy growth, it is
necessary that the difference between the lattice constants of both the
films be set to 5% or less. If the difference of the lattice constants is
5% or more, misfit dislocation is caused or strains are produced in the
magnetic film so that the magnetic anisotropy is unfavorably reduced.
The perpendicular magnetic film may be made of a Co-alloy containing, as an
alloying element, at least one element selected from Cr, Ta, Pt, Pd, Si,
V, Nb, W, Mo, Hf, Re, Zr, B, P, Ru and the like. In this example, two
perpendicular magnetic layers having different compositions are stacked
with each other. In the lower perpendicular magnetic layer 14, the total
amount of nonmagnetic elements added to Co is larger than in the upper
perpendicular magnetic layer 15, so thait the lower perpendicular magnetic
layer 14 functions to adjust the magnetic anisotropic energy Ku to a small
value and precipitate the nonmagnetic elements in a larger amount in the
crystal boundary.
The upper perpendicular magnetic layer 15 is formed in such a manner that
hetero-epitaxy relationship relative to the lower perpendicularmagnetic
layer 14 is maintained. Crystallographicically, continuous crystal growth
is realized from the second underlayer 13 to the surface of the upper
perpendicular magnetic layer 15.
These magnetic films are polycrystal films. In order that these films have
a high linear recording density property and a low noise property, they
have the average grain size of 15 nm or less and a structure wherein
nonmagnetic elements are preferentially segregated in the crystal grain
boundary of in particular the lower perpendicular magnetic layer 14.
Since this perpendicular magnetic layer 14 has on its crystal grain
boundary a segregation layer in the longitudinal direction, magnetic
interaction is small. In order to reduce medium noises, the upper
perpendicular magnetic layer 15 having a relatively large magnetic
anisotropic energy Ku is formed on this perpendicular magnetic layer 14,
as described above. A protective film 16 is formed on the upper
perpendicular magnetic layer 15.
FIGS. 2-4 are schematic views of sections of other examples of
perpendicular magnetic recording media according to the present invention.
A perpendicular magnetic recording medium of a second example, the
sectional structure of which is shown in FIG. 2, is a medium wherein two
underlayers composed of a first underlayer 22 and a second underlayer 23
are formed on a nonmagnetic substrate 21 and a magnetic film is formed
thereon. This magnetic film is a film wherein a nonmagnetic interlayer 25
or a weakly magnetic interlayer 25 having a saturation magnetization Ms of
50 emu/cc or less, which has a thickness of 0.1-5 nm, is disposed between
two stacked perpendicular magnetic layers of a lower perpendicular
magnetic layer 24 and an upper perpendicular magnetic layer 26. This
magnetic film has an advantage of reducing medium noises.
Crystallographicically, the interlayer 25 is hetero-epitaxially grown onto
the upper and lower perpendicular magnetic film 24 and 26. The thickness
of the interlayer 25 is desirably from 0.5 to 5 nm, and more desirably
from 1 to 3 nm. Such a structure makes it possible to control the crystal
grain size and the orientation of the perpendicular magnetic film highly,
so that a lower noise property can be realized.
A protective film 27 is formed on the surface of the upper perpendicular
magnetic film 26. As materials of the upper underlayer 22, the second
underlayer 23, the lower perpendicular magnetic film 24 and the upper
perpendicular magnetic film 26 and the like, the same as materials of the
corresponding elements of the medium structure of the first example
illustrated in FIG. 1 are used.
The medium structure of a third example according to the present invention,
which is illustrated in FIG. 3, corresponds to a structure in which a
metal film 36 is deposited on the magnetic film (the upper perpendicular
magnetic film 15) of the perpendicular magnetic recording medium of the
first example illustrated in FIG. 1. That is, in this medium structure,
two underlayers composed of a first underlayer 32 and a second underlayer
33 are formed on a nonmagnetic substrate 31, and further bilayer
perpendicular magnetic film composed of lower and upper perpendicular
magnetic layers 34 and 35 is formed thereon. A metal film 36 is formed on
the upper perpendicular magnetic film 35 and a protective film 37 is
formed thereon.
As the material of the underlayers and the perpendicular magnetic film, the
same materials as described concerning the first example can be used. As
the metal film 36, the following can be used: a simple metal of Pt, Pd,
Ir, Re, Ru or Hf; an alloy made mainly of any one(s) of these metal
elements; stack films of a Co film or a Co-alloy film, and a film of a
simple metal of any one(s) of these metal or an alloy film made mainly of
any one(s) of these metal elements; or an amorphous magnetic material film
containing a rare-earth element.
The medium structure of a fourth example according to the present
invention, which is illustrated in FIG. 4, corresponds to a structure in
which a metal film 47 is deposited on the magnetic film (the upper
perpendicular magnetic film 26) of the perpendicular magnetic recording
medium of the second example illustrated in FIG. 2. A nonmagnetic
substrate 41, a first underlayer 42, a second underlayer 43, a lower
perpendicular magnetic layer 44, an interlayer 45, an upper perpendicular
magnetic layer 2046, and a protective film 48 correspond to the
nonmagnetic substrate 21, the first underlayer 22, the second underlayer
23, the lower perpendicular magnetic layer 24, the interlayer 25, the
upper perpendicular magnetic layer 26, and the protective film 27,
respectively.
As a metal film 47, the following can be used: a simple metal of Pt, Pd,
Ir, Re, Ru or Hf; an alloy made mainly of any one(s) of these metal
elements; stack films of a Co film or a Co-alloy film, and a film of a
simple metal of any one(s) of these metal or an alloy film made mainly of
any one(s) of these metal elements; or an amorphous magnetic material film
containing a rare-earth element.
The medium structures illustrated in FIGS. 1-4 make it possible to reduce
long and short range, magnetization fluctuations present in the surface of
the perpendicular magnetic film and make the pitch of the microscopic
magnetic fluctuations shorter than the recording bit length, resulting in
a reduction in medium noises.
According to the present invention, noises of the perpendicular magnetic
recording medium can be reduced to obtain a high S/N ratio. Thus, it
becomes possible to obtain a high-density magnetic disk apparatus, and in
particular attain high-density magnetic recording which can realize a
recording density of 10 Gb/in..sup.2 or more. As a result, it becomes easy
to make the apparatus compact and make its capacity large.
The following will more specifically describe the present invention.
Examples 1-5 are examples concerned with the invention which can attain
the first object, and Examples 6-10 are examples concerned with the
invention which can attain the second object.
EXAMPLE 1
A glass substrate of 2.5 in. diameter was used to deposit thin films
necessary for a recording medium sequentially on this substrate by a film
depositing method according to DC magnetron sputtering. Thus, a magnetic
recording medium having the sectional structure shown in FIG. 1 was
produced.
Namely, the first underlayer 12, the second underlayer 13, the lower
perpendicular magnetic layer 14, the upper perpendicular magnetic layer 15
and the protective film 16 were formed in this order on the substrate 11.
The conditions for depositing the respective films by the sputtering were
as follows.
Concerning targets used in the sputtering, a Ti--10.2 atomic % Cr target, a
Co--34 atomic % Cr target, a Co--17 atomic % Cr--5 atomic % Ta target,
Co--10 atomic % Cr--10 atomic % Pt target, and a carbon target were used
to form the first underlayer 12, the second underlayer 13, the lower
perpendicular magnetic layer 14, the upper perpendicular magnetic layer 15
and the protective film 16, respectively.
Under the conditions of a sputtering Ar gas pressure of 3 mTorr, a
sputtering power of 10 W/cm.sup.2 and a substrate temperature of
250.degree. C., the following were deposited: a CrTi film, as the first
underlayer 12, of 30 nm thickness; a CoCr film, as the second underlayer
13, of 30 nm thickness; the lower perpendicular magnetic layer 14 of 30 nm
thickness; the upper perpendicular magnetic layer 15 of 2 nm thickness;
and a carbon film, as the protective film 16, of 10 nm thickness.
Samples of perpendicular magnetic media were produced under the same film
depositing conditions as above except that the thickness of the upper
perpendicular magnetic layer 15 was set to 5 nm, 10 nm, 15 nm, 20 nm, 30
nm or 40 nm.
As comparative samples, perpendicular magnetic media were produced in one
of which the upper perpendicular magnetic layer 15 was not formed and in
the other of which the thickness of the upper perpendicular magnetic layer
15 was set to 50 nm.
The magnetic properties of the upper and lower perpendicular magnetic
layers 15 and 14 were measured, and then the following results were
obtained. Concerning the lower perpendicular magnetic layer 14, Ms=385
emu/cc and Ku=1.8.times.10.sup.6 erg/cc, and concerning the upper
perpendicular magnetic layer 15, Ms=675 emu/cc and Ku=4.1.times.10.sup.6
erg/cc.
The saturation magnetization Ms of the second underlayer 13 was 12 emu/cc.
Analysis using an electron microscope proved that the crystal grain sizes
of these perpendicular magnetic layers were from 8 to 14 nm and Cr having
an average width of 1 nm was segregated in an amount of 26-28 atomic %
between the crystal grains.
The difference between the lattice constant of the second underlayer 13 and
that of the lower perpendicular magnetic layer 14 was 3.2 %.
A dual element magnetic head was used to evaluate the read/write
characteristics of these magnetic recording media. The gap length of the
recording head was 0.2 .mu.m, the shield gap of the magneto-resistive
reading head was 0.2 .mu.m and the spacing at the time of the measurement
was 0.06 .mu.m. The recording performance of the media was evaluated by
measuring a recording density (D.sub.50) at which the signal output
decreases by a half of the signal output at a low recording density. The
S/N ratio when magnetic recording was conducted at 20 kFCI was evaluated
as a value relative to the S/N ratio of the comparative sample which did
not have the upper perpendicular magnetic layer 15. These results are
shown Table 1.
TABLE 1
Compara-
tive
example The present invention
Lower 30 30 30 30 30 30 30 30 30
perpen- nm nm nm nm nm nm nm nm nm
dicular
mag-
netic
layer
Upper None 50 2 5 10 15 20 30 40
perpen- nm nm nm nm nm nm nm nm
dicular
mag-
netic
layer
D.sub.50 155 186 265 250 248 240 236 225 220
(kFCl)
S/N 1 1.22 2.53 2.22 2.41 2.56 2.43 2.31 2.10
(relative
value)
The magnetic media of the present example had a greatly improved D.sub.50
and an improved S/N ratio as compared with the comparative examples. Thus,
it was understood that the former media were preferable as high-density
magnetic recording media. The magnetic media produced in the present
example were used to produce a 2.5 in. magnetic recording/reading device
using an MR head as a reading element. Under the condition that its areal
recording density was 10 Gb/in..sup.2, an error rate of 10.sup.-9 was able
to be obtained. Thus, it was ascertained that this device was operated as
a ultra-high-density recording/reading device.
EXAMPLE 2
A silicon substrate of 2.5 in. diameter was used to produce a perpendicular
magnetic recording medium having a sectional structure illustrated in FIG.
2 by DC magnetron sputtering. The first underlayer 22, the second
underlayer 23, the lower perpendicular magnetic layer 24, the interlayer
25, the upper perpendicular magnetic layer 26 and the protective film 27
were formed in this order on the substrate 21.
Concerning targets used in the sputtering, a Ge target, a Co--35 atomic %
Ru target, a Co--15 atomic % Cr--6 atomic % Pt--3 atomic % Y target, a
Co--45 atomic % Ru target, a Co--14 atomic % Cr--8 atomic % Pt target, and
a carbon target were used to form the first underlayer 22, the second
underlayer 23, the lower perpendicular magnetic layer 24, the interlayer
25, the upper perpendicular magnetic layer 26 and the protective film 27,
respectively.
The saturation magnetization of the Co--35 atomic % Ru layer as the second
underlayer 23 was not more than 15 emu/cc. Thus, a weakly magnetic film
was obtained.
Under the conditions of a sputtering Ar gas pressure of 3 mTorr, a
sputtering power of 10 W/cm.sup.2 and a substrate temperature of
280.degree. C., the following were deposited: A Ge film, as the first
underlayer 22, of 30 nm thickness; a Co--Ru film, as the second underlayer
23, of 15 nm thickness; the lower perpendicular magnetic layer 24 of 30 nm
thickness; the interlayer 25 of 0.1 nm thickness; Co--Cr--Pt film, as the
upper perpendicular magnetic layer 26, of 2 nm thickness; and a carbon
film, as the protective film 27, of 10 nm thickness. Thus, a perpendicular
magnetic recording medium was produced which had a sectional structure
illustrated in FIG. 2.
Samples of perpendicular magnetic media were produced under the same film
depositing conditions as above except that the thickness of the interlayer
25 was set to 1 nm, 2 nm, 3 nm, or 5 nm.
As a comparative sample, a monolayer perpendicular magnetic medium was
produced which had no lower perpendicular magnetic layer 24 and but had a
Co--Cr--Pt film of 35 nm, which was used for the forming of the upper
perpendicular magnetic layer 26. The conditions for forming the
underlayers and the protective film of this comparative example were the
same as in the example.
The magnetic properties of the upper and lower perpendicular magnetic
layers 26 and 24 were measured, and then the following results were
obtained. Concerning the lower perpendicular magnetic layer 24, Ms=370
emu/cc and Ku=2.0.times.10.sup.6 erg/cc, and concerning the upper
perpendicular magnetic layer 26, Ms=600 emu/cc and Ku=4.3.times.10.sup.6
erg/cc. The saturation magnetization Ms of the interlayer 25 was 0 emu/cc.
Analysis using an electron microscope proved that the average grain size of
crystal grains, measured in the surface of the upper perpendicular
magnetic layer 26, was 11 nm and that Cr atoms were segregated in an
amount of 27 atomic % in the crystal grain boundary of the lower
perpendicular magnetic layer 24 with an average width of 1.2 nm.
The difference between the lattice constant of the second underlayer 23 and
that of the lower perpendicular magnetic layer 24 was 3%.
A vibrating sample magneto-meter (VSM) and a dual element magnetic head
were used to evaluate the coercive force Hc and the read/write
characteristics of these magnetic recording media. The gap length of the
recording head was 0.2 .mu.m, the shield gap of the giant
magneto-resistive (GMR) reading head was 0.15 .mu.m and the spacing at the
time of the measurement was 0.04 .mu.m.
The recording performance of the media was evaluated by measuring a
recording density (D.sub.50) at which the signal output decreased by a
half of the signal output at a low recording density. The S/N ratio when
magnetic recording was conducted at 20 kFCI was evaluated as a value
relative to the S/N ratio of the comparative sample. These results are
shown in Table 2.
TABLE 2
Comparative
example The present invention
Lower None 30 30 30 30 30
perpen- nm nm nm nm nm
dicular
magnetic layer
Interlayer None 0.1 1 2 3 5
nm nm nm nm nm
Upper 35 nm 2 2 2 2 2
perpen- nm nm nm nm nm
dicular magnetic
layer
HC (kOe) 2.8 2.7 2.4 2.5 2.4 2.3
D.sub.50 (kFCl) 185 268 250 245 220 215
S/N 1 2.8 2.1 2.0 1.75 1.2
(relative value)
The magnetic recording media of the present example had greatly improved
D.sub.50 and S/N ratio as compared with the comparative examples. Thus, it
was understood that the former media were preferable as high-density
magnetic recording media. The magnetic media produced in the present
example were used to produce a 2.5 in. magnetic recording/reading device
using a GMR head as a reading element. Under that condition that its areal
recording density was 20 Gb/in..sup.2, an error rate of 10.sup.-9 was able
to be obtained. Thus, it was ascertained that this device was operated as
a ultra-high-density recording/reading device.
EXAMPLE 3
A glass substrate of 2.5 in. diameter was used to produce a perpendicular
magnetic recording medium having a sectional structure illustrated in FIG.
3 by DC magnetron sputtering. The first underlayer 32, the second
underlayer 33, the lower perpendicular magnetic layer 34, the upper
perpendicular magnetic layer 35, the metal film 36 and the protective film
37 were formed in this order on the substrate 31.
Targets used in the sputtering were as follows. A Ti target, a Co--30
atomic % Cr--10 atomic % Ru target, a Co--17 atomic % Cr--1 atomic % Y--3
atomic % Ta target, a Co--18 atomic % Cr--10 atomic % Pt target, a Pt
target, and a carbon target were used for the first underlayer 32, the
second underlayer 33, the lower perpendicular magnetic layer 34, the upper
perpendicular magnetic layer 35, the metal film 36 and the protective film
37, respectively.
Under the conditions of a sputtering Ar gas pressure of 3 mTorr, a
sputtering power of 10 W/cm.sup.2 and a substrate temperature of
250.degree. C., the following were deposited: a Ti film, as the first
underlayer 32, of 30 nm thickness; a Co--Cr--Ru film, as the second
underlayer 33, of 20 nm thickness; a Co--Cr--Y--Ta film, as the lower
perpendicular magnetic layer 34, of 20 nm thickness; a Co--Cr--Pt film, as
the upper perpendicular magnetic layer 35, of 1 nm thickness; a Pt film,
as the metal film 36, of 0.5 nm thickness; and a carbon film, as the
protective film 37, of 7 nm thickness.
Perpendicular magnetic media were produced in the same manner as above
except that a Pd film (1 nm), an Ir film (1.5 nm), a Re film (0.1 nm), a
Ru film (1.2 nm) and a Co/Pt multilayer film (3 nm) were formed,
respectively, as the metal film 36 instead of the Pt film. This Co/Pt
multilayer film was formed in such a manner that its total thickness would
be 3 nm by repeating the cycle that a Co target and a Pt target were
alternately used to form layers, each thickness of which was 0.5 nm, 6
times.
As comparative samples, the same perpendicular magnetic media as in the
example were produced except that the upper perpendicular magnetic layer
35 and the metal film 36 were omitted.
The magnetic properties of the upper and lower perpendicular magnetic
layers 35 and 34 were measured, and then the following results were
obtained. Concerning the lower perpendicular magnetic layer 34, Ms=340
emu/cc and Ku=1.5.times.10.sup.6 erg/cc, and concerning the upper
perpendicular magnetic layer 35, Ms=420 emu/cc and Ku=3.0.times.10.sup.6
erg/cc.
Analysis using an electron microscope proved that the average grain size of
crystal grains, measured in the surface of the upper perpendicular
magnetic layer 35, was 12 nm and that Cr atoms were segregated in an
amount of 26-30 atomic % in the crystal grain boundary of the lower
perpendicular magnetic layer 34 with an average width of 1 nm.
The difference between the lattice constant of the second underlayer 33 and
that of the lower perpendicular magnetic layer 34 was 4%.
The read/write characteristics of these magnetic recording media were
measured in the same manner as in Example 2. The results are shown in
Table 3.
TABLE 3
Compara-
tive
example The present invention
Lower 20 20 20 20 20 20 20 20
perpen- nm nm nm nm nm nm nm nm
dicular
magnetic
layer
Upper None 1 1 1 1 1 1 1
perpen- nm nm nm nm nm nm nm
dicular
magnetic
layer
Metal film None None Pt Pd Ir Re Ru Co/Pt
0.5 1 1.5 0.1 1.2 3
nm nm nm nm nm nm
Hc (kOe) 2.3 2.5 2.5 2.5 2.4 2.5 2.4 2.9
D.sub.50 (kFCl) 190 220 235 240 243 251 240 265
S/N 1 1.2 2.1 2.2 2.0 2.3 2.4 2.2
(relative
value)
Error 1 .times. 3 .times. 1 .times. 3 .times. 5 .times. 1 .times. 8
.times. 6 .times.
rate 10.sup.-6 10.sup.-6 10.sup.-9 10.sup.-10 10.sup.-10
10.sup.-9 10.sup.-10 10.sup.-10
The magnetic recording media of the present example had greatly improved
Dso and S/N ratio as compared with the comparative examples. Thus, it was
understood that the former media were more preferable as high-density
magnetic recording media. The magnetic media produced in the present
example were used to produce a 2.5 in. magnetic recording/reading device
using, as a reading element, a high-sensitivity reading head using a
magneto-resistive head applying magnetic tunneling effect. Under that
condition that its areal recording density was 30 Gb/in..sup.2, an error
rate of 10.sup.-9 was able to be obtained as shown in Table 3. Thus, it
was ascertained that this device was operated as a ultra-high-density
recording/reading device.
EXAMPLE 4
Perpendicular magnetic recording medium having a sectional structure
illustrated in FIG. 4 was produced in the same manner as in Example 2
except that a multilayer metal film 47 of (Co--10 atomic % Cr--3 atomic %
Ta)/(Pt--45 atomic % Re), which had a thickness of 5 nm, was deposited on
the upper perpendicular magnetic recording layer in the perpendicular
magnetic recording medium produced in Example 2.
Namely, the first underlayer 42, the second underlayer 43, the lower
perpendicular magnetic layer 44, the interlayer 45, the upper
perpendicular magnetic layer 46, the multilayer metal film 47 and the
protective film 48 were formed sequentially on the substrate 41.
The (Co--10 atomic % Cr--3 atomic % Ta)/(Pt--45 atomic % Re) multilayer
metal film 47 was formed in such a manner that its total thickness would
be 5 nm by repeating the cycle that a Co--Cr--Ta target and a Pt--Re
target were alternately used to form layers, each thickness of which was
0.25 nm, 10 times.
As a comparative example, a perpendicular magnetic recording medium was
produced in which the metal film 47, the lower perpendicular magnetic
layer 44 and the interlayer 45 were not formed. Their characteristics were
measured under the same recording/reading conditions as in Example 2. The
results are shown in FIG. 4.
TABLE 4
Com-
parative
example The present invention
Lower None 30 nm 30 nm 30 nm 30 nm 30 nm
perpendicular
magnetic
layer
Interlayer None 0.1 1 2 3 5
nm nm nm nm nm
Upper 35 nm 2 nm 2 nm 2 nm 2 nm 2 nm
perpendicular
magnetic
layer
Metal film None 5 nm 5 nm 5 nm 5 nm 5 nm
Hc (kOe) 2.8 3.1 2.9 2.7 2.4 2.3
D.sub.50 (kFCl) 185 270 263 230 220 228
S/N (relative 1 3.2 2.6 2.4 2.5 1.9
value)
Error rate 8 .times. 1 .times. 1 .times. 9 .times. 8 .times. 1 .times.
10.sup.-5 10.sup.-9 10.sup.-9 10.sup.-10 10.sup.-10
10.sup.-9
The magnetic recording media of the present examples had greatly improved
D.sub.50 and S/N ratio as compared with the comparative example. Thus, it
was understood that the former media were more preferable as high-density
magnetic recording media. Under that condition that its areal recording
density was 20 Gb/in..sup.2, an error rate of 10.sup.-9 was able to be
obtained as shown in Table 4. Thus, it was ascertained that this device
was operated as a ultra-high-density recording/reading device.
EXAMPLE 5
The perpendicular magnetic recording media produced in Example 3 and a dual
element head having a high-sensitivity reading element using a giant
magneto-resistance (GMR) were used to make a magnetic storage apparatus.
As illustrated in FIG. 5A, which is a schematic plane view, and FIG. 5B,
which is a cross section along an AA line in FIG. 5A, this magnetic
storage apparatus is an apparatus having a well known structure, which has
a magnetic recording medium 51 which is rotated and driven by a magnetic
recording medium driving unit 52, a magnetic head 53 which is held by a
magnetic head driving unit 54 and records data on the magnetic recording
medium 51 and reads data therefrom, and a recording/reading signal
processing unit 55 for processing recording data and reading data from the
magnetic head 53.
The track width of the recording head was set to 0.4 .mu.m, the track width
of the GMR head element for reading was set to 0.32 .mu.m, and the spacing
between the head and the medium was set to 15 .mu.m. As a signal
processing, the PR5 method was adopted. When the apparatus was operated
under the condition of an areal recording density of 30 Gb/in..sup.2,
excellent read/write characteristics of error rates of 10.sup.-9 or less
were obtained in all of the perpendicular magnetic recording media.
EXAMPLE 6
A sputtering method was used to form a Ti--10 atomic % Cr alloy film (the
first underlayer) of 30 nm thickness on a disk substrate made of Al--Mg
alloy to which a nickel(Ni) and phosphorus (P) alloy plating film was
applied. Thereafter, the second underlayer was formed which was composed
of a nonmagnetic Co--Cr alloy film having a composition of Co--35 atomic %
Cr and a thickness of 0.02 .mu.m. The underlayers composed of these two
layers were made at a substrate temperature of 200.degree. C.
Thereafter, a quadruple alloy of Co--19 atomic % Cr--10 atomic % Pt--2
atomic % Ta and of 30 nm thickness was formed as a perpendicular magnetic
recording film.
Furthermore, a magnetic film of Co--18 atomic % Sm and of 2 nm thickness
was formed thereon at a substrate temperature of 300.degree. C. in order
to prohibit generation of reversed domains in the surface layer.
At last, a carbon film of 15 nm thickness was formed as a protective film.
The sample produced in this manner was referred to as disk S1.
A sample was produced under the same condition as for the disk S1 except
that the thickness of Co--Sm alloy for prohibiting reversed domains in the
surface layer of the perpendicular magnetic recording film was set to 1
nm. This disk was referred to as disk S2.
As a comparative example, a sample having the same structure as disk Si
except that the Co--Sm film was not formed was produced under the same
condition. This sample was referred to as disk R1.
It was ascertained with an X-ray diffractometer that in the perpendicular
magnetic recording films (Co--19 atomic % Cr--10 atomic % Pt--2 atomic %
Ta) of the disks S1, S2 and R1 produced in the manners all of their
crystal structures had a hexagonal close packed structure and their c axis
was oriented perpendicularly to their film surface.
The magnetic characteristics of the samples produced in this way were
measured with a vibrating sample magneto-meter (VSM) to obtain their
saturation magnetization (Ms) and coercive force (Hc). The direction along
which the magnetic field was applied was set to the direction
perpendicular to the film plane. The results are shown as magnetization
curves in FIG. 6, and are together shown in Table 5.
As is evident from FIG. 6, in the disk S1 as the intensity of the magnetic
field decreased, the magnetization decreased slowly due to the reduced
magnetization of the surface layer with in-plane axis of easy
magnetization. However, even if the magnetic field direction was reversed,
this tendency did not change up to about 400 Oe.
When the intensity of the reversed magnetic field reached 400 Oe, the
magnetization curve became a shoulder-like form. When the intensity of the
magnetic field became more than 400 Oe, irreversible magnetization
reversal occurred so that the magnetization was suddenly reduced. In other
words, in the disk S1, reversed domains were generated at about 400 Oe in
the perpendicular magnetic film.
On the other hand, in the comparative disk R1 the shoulder-like portions of
the magnetization curve were present in the first and fourth quadrants.
Thus, irreversible magnetization reversal started just before the magnetic
field direction was reversed. As described above, a great difference was
observed in the intensities of the magnetic fields at the position of the
should-like portions between the disk S1 of the present invention and the
disk R1 of the comparative example.
The magnetization curve of the disk S2 having the Co--Sm film of 1 nm
thickness for prohibiting the generation of reversed domains in the
surface layer of the perpendicular magnetic recording film had
substantially the same form as that of the disk S1. Thus, it was
ascertained that same effect was obtained in the case that the thickness
of the Co--Sm film was a small value of 1 nm, as well.
The film formed to prohibit the reversed domains in the surface layer of
the perpendicular magnetic recording film is an in-plane easy
magnetization film. For this reason, when perpendicular magnetic recording
is conducted, some trouble may happen. Therefore, it is desired that the
thickness of the film deposited on the surface is made as thin as
possible.
Next, a magnetic recording/reading tester was used to evaluate the
read/write characteristics of these disks S1, S2 and R1. A magnetic head
used in the recording and reading was a thin film head wherein its gap
length was 0.2 .mu.m, its track width was 4.5 .mu.m and its coil-turned
number was 30.
Reproduced output and medium noises were measured in the case that "all 1",
signals were recorded under the conditions that the spacing between the
air-bearing face of the head and the surface of the medium, that is, the
floating height, was 0.04 .mu.m, the circumferential speed was 10 m/s and
the linear recording density was 200 kFCI. After recording was conducted
on the disks at 200 kFCI and then the disks were allowed to be left
without any operation stand. Thus, the change in reproduced output was
examined with the passage of time. The results are shown in Table 5.
As is evident from Table 5, when the reproduced outputs after 100 hours of
the disks S1 and S2 according to the present example are compared with
that of the comparative disk R1, it can be found that while the output of
the disk R1 decreased by 8%, the outputs of the disks S1 and S2 decreased
by 0.5% and 0.8%, respectively. Thus, the decrease in the outputs of the
disks S1 and S2 can hardly be observed.
Concerning the reproduced output and the medium noises, the disks S1 and S2
were more excellent than the comparative disk R1. It can be therefore
understood that the present invention has an advantage for improving
read/write characteristics.
The above results demonstrate that as the magnetic field at which
irreversible magnetization occurs, that is, the polarity of the
shoulder-like portion in the magnetization curve is opposite to the
direction of the magnetic field initially applied and the absolute value
thereof is larger, the read/write characteristics for magnetic recording
media are more excellent and stability against thermal fluctuation is
higher.
The reason why such magnetic characteristics were obtained in the disks S1
and S2 is that the magnetic film whose anisotropic magnetic field is large
and whose direction of easy magnetization is in-plane is formed as a film
for prohibiting the generation of reversed domains on the surface of the
perpendicular magnetic recording film.
It is presumed that even if this film for prohibiting the generation of
reversed domains has a very small thickness of 1-2 nm, this film has a
great effect for prohibiting nucleation sites which can cause irreversible
magnetization reversal in the film surface, that is, the generation of
reversed domains in the surface layer of the perpendicular magnetic
recording film.
It is considered that these reversed domains mainly cause medium noises,
and that the medium noises are also reduced as a result of difficulty in
generating the reversed domains.
It is also considered that difficulty in causing the reversed domains
similarly produces a good effect for improving thermal stability.
Since the thickness of the Co--Sm film as the film for prohibiting the
reversed domains is a small value of 1-2 nm in the present example, the
crystal structure and the in-plane coercive force of the Co--Sm film were
not able to be identified. In order to examine the crystal structure and
magnetic characteristics, a Co--35 atomic % Cr, which was an underlayer,
was formed by sputtering, and then a Co--Sm film of 30 nm thickness was
formed. As a result, it was ascertained that its crystal structure was
amorphous and it was also ascertained from the measurement of its magnetic
characteristics that this film had an in-plane axis of easy magnetization
and its in-plane coercive force was about 800 Oe.
EXAMPLE 7
The following will describe an example in which an Fe--Nd--B magnetic film
was formed on the surface of a perpendicular magnetic recording film. The
method for producing a sample was the same as in Example 6. In the present
example, however, a quadruple alloy of Co--19 atomic % Cr--10 atomic %
Pt--2 atomic % Ta was formed as a perpendicular magnetic recording film
and then a magnetic film (referred to as a surface magnetic film) having a
composition of Fe--12 atomic % Nd--8 atomic % B and a thickness of 2 nm
was formed as a magnetic film deposited on the surface of this
perpendicular magnetic recording film at a substrate temperature of
350.degree. C. Thereafter, a carbon protective film of 15 nm thickness was
formed to produce a disk S3.
The magnetic characteristics and the read/write characteristics of the disk
S3 are together shown in Table 5. As is evident from Table 5, in the disk
S3 the value of its nucleation magnetization became negative and reversed
domains were more difficult to be generated than the comparative disk R1.
Following this, both of read/write characteristics and stability against
thermal fluctuation were improved. These effects show that the Fe--Nd--B
magnetic film also has an effect of prohibiting reversed domains,
similarly to the Sm--Co magnetic film, but that this effect is smaller
than that of the disks S1 and S2.
In order to examine the crystal structure and magnetic characteristics of
the Fe--Nd--B film of this sample, an Fe--12 atomic % Nb--8 atomic % B
film of 30 nm thickness was directly formed on the underlayer. As a
result, it was ascertained that the Fe--Nd--B film had an in-plane axis of
easy magnetization with crystal structure of amorphous and its in-plane
coercive force was about 300 Oe.
EXAMPLE 8
The following will describe an example in which a magnetic film with an
in-plane axis of easy magnetization was formed on the back face, that is,
the substrate side of a perpendicular magnetic recording film (on the
perpendicular magnetic recording medium surface facing to the substrate).
The method for producing the sample was the same as in Example 6. In the
present example, however, a nonmagnetic Co--Cr film of Co--35 atomic % Cr
was formed as the second underlayer and subsequently an in-plane easy
magnetization film of 18 atomic % Sm and of 2 nm thickness was formed at a
substrate temperature of 300.degree. C.
Thereafter, a perpendicular magnetic film of Co--19 atomic % Cr--10 atomic
% Pt--2 atomic % Ta of 30 nm thickness was formed as a magnetic recording
film, and then a carbon film of 15 nm thickness was formed as a protective
film thereon. In short, in the present example the in-plane axis of easy
magnetization film was formed on the back surface of the perpendicular
magnetic recording film.
The sample produced in this manner was referred to as disk S4. Its
magnetization curve and read/write characteristics were measured in the
same manner in Example 6. The results are shown in Table 5. As is evident
from Table 5, in the disk S4 its nucleation field exhibited a large value
of -415 Oe, similarly to the disks S1 and S2, and reversed domains were
not easily generated. The read/write characteristics and the reduction in
output after 100 hours of the disk S4 were also more excellent than the
comparative disk R1.
EXAMPLE 9
A sample was produced wherein in-plane easy magnetization films were formed
on the front surface and the back surface of a perpendicular magnetic
recording film. The method for producing the sample of the present example
was a combination of those in Examples 6 and 8. Its film structure was a
structure wherein in-plane easy magnetization films of Co--18 atomic % Sm
and of 2 nm thickness were formed on the back surface and the front
surface of a perpendicular magnetic film of Co--19 atomic % Cr--10 atomic
% Pt--2 atomic % Ta.
This disk was referred to as disk S5. Its magnetic characteristics and
read/write characteristics were measured in the same manner as in Example
6. The results are shown in Table 5. As is evident from Table 5, by
depositing the in-plane easy magnetization films on the front and back
surfaces of the perpendicular magnetic film, its nucleation magnetization
became a larger value of--520 Oe than the media wherein the in-plane easy
magnetization films film was formed only on their single surface. The
read/write characteristics and the reduction in output after 100 hours of
the disk S5 were also further improved.
TABLE 5
(No. 1)
Magnetic properties
Coercive Nucleation
force Rectangularity magnetization*
Disk (Oe) Ratio (Oe)
S1 2730 0.90 -430
S2 2690 0.87 -370
S3 2530 0.90 -123
S4 2720 0.92 -415
S5 2750 0.85 -520
R1 2540 0.85 +115
(No. 2)
Read/write characteristics**
Relative Reduction in
Relative medium Relative output after
regenerative noise S/N 100 hours
Disk output (dB) (dB) (dB) (%)
S1 +1.4 -1.5 +2.9 0.5
S2 +1.5 -1.6 +3.1 0.8
S3 +0.3 -0.5 +0.8 2.7
S4 +1.0 -0.5 +1.5 0.7
S5 +1.5 -2.0 +3.5 0.2
R1 0 0 0 8.0
*Concerning the signs in Table 5, the direction of the magnetic field
initially applied is set to "+". The nucleation magnetization means an
intensity of the magnetization at which irreversible magnetization
reversal starts to arise in the magnetization curves, that is, a
magnetization at the position of the shoulder-like portion in the
magnetization curve.
**The value of the comparative disk R1 was set to 0 dB.
EXAMPLE 10
FIG. 7 is a schematic view of an example of the magnetic disk device
according to the present invention. In a head disk assembly 4, plural
magnetic disks 1 are fitted onto a spindle axis, and are rotated at a high
speed by a spindle 5.
As these disks 1, the disks produced in Examples 6-10 are used. Magnetic
heads for recording/reading signals are arranged oppositely to the
magnetic recording surfaces of the disks, and one of them functions as a
servo head.
The magnetic heads 2 are transferred in the substantial radius direction of
the magnetic disks 1 by an actuator 6 through a head stuck assembly 3.
Furthermore, the present device has a read/write channel 7 for
reading/writing data, a signal processor 8 for processing the data, a head
disk controller 9 for controlling these units and the driving units, an
interface 10 for giving data to the device and taking data therefrom, and
the like.
This magnetic disk device was used to read data on the magnetic disks
produced in Examples 6-10, so that sufficiently high regenerative output
and low medium noises were able to be obtained in all of the disks. Even
if information was recorded on the disks and the disks were allowed to
stand for not less than 100 hours, a reduction in the reproduced output
was hardly observed and thermal stability was also excellent.
Top